Wireless communication systems are widely deployed to provide various types of communication such as voice and data. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. A CDMA system provides certain advantages over other types of systems, including increased system capacity.
A CDMA system may be designed to support one or more CDMA standards such as (1) the “TIA/EIA-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (the IS-95 standard), (2) the standard offered by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (3) the standard offered by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “C.S0002-A Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” and the “C.S0024 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 standard), and (4) some other standards. Non-CDMA systems include the AMPS and GSM systems.
When a mobile station first acquires a system, one or more available base stations or cells are identified by the mobile station. Typically a single cell is selected as the serving cell. When the mobile station is not actively communicating for a voice call or data session, it is said to be in idle mode. The mobile station the serving cell to determine if an event, such as an incoming call, would require the mobile station to leave idle mode. As the communication channel between the serving cell and the mobile station changes, the mobile station must periodically test the channel to determine if that cell is still suitable. For example, the communication channel will change as the mobile station moves between cells within a system or between one or more neighboring systems. Occasionally a new serving cell will be selected, a process known as cell reselection, or idle mode handoff.
During idle mode, a mobile station may go into a low-power, or “sleep” state, to reduce power consumption. A mobile station may discontinue reception during sleep state to allow receive circuitry to be disabled. Periodically, the mobile station must come out of sleep state, or “wake up”, reacquire the serving cell, and monitor signals therefrom to determine if an incoming call is being directed to the mobile station. For example, a page indicator may be directed to a mobile station, to indicate whether the mobile station should enter active communications, or whether the low-power state can be reentered. During this time, a cell reselection process may be performed to determine if cell reselection is necessary. It is desirable for the mobile station to go back to the sleep state as soon as possible if it is to remain in idle mode, in order to conserve power. If a cell reselection is necessary, the mobile station may remain awake longer, in order to process the reselection.
It is desirable for a mobile station to wake up no sooner than necessary to receive the page indicator. However, the time required to reacquire the serving cell, or identify a reselection candidate if the serving cell has become unavailable, will vary according to changes in the communication channel conditions. Power conservation, and the associated benefits of reduced battery requirements and increased standby times, can be increased by minimizing the portion of a sleep cycle spent in reacquisition and reselection procedures. Concurrently, however, other system considerations may require adequate assessments of channel conditions associated with various neighbor cells, as well as timely and accurate response to page indicators. There is therefore a need in the art for cell reacquisition and reselection that increases time spent in low-power mode while effectively monitoring neighbor cells.